SAMPLING AND WEIGHING. 113 



For weighing gold, silver, or platinum, the troy weight is 

 sometimes used ; for weighing other metals, avoirdupois. 

 The French decimal system of grammes and decimals of a 

 gramme is convenient for both. (See APPENDIX.) 



The management of the button balance requires very 

 great care, and should never be used except for the precious 

 metals, as the ores, fluxes, &c., must be weighed on a less 

 delicate balance. To adjust and thoroughly understand the 

 reading of the button balance needs instruction, and no one 

 should use one until the working of it has been explained. 

 It may be well, however, to mention that the glass slide 

 should always be kept down except during the weighing 

 operation, and that the apparatus should never be by any 

 means exposed to acid or other deleterious fumes. 



A very good plan is to use the conventional assay ton 

 weights in weighing the ore, as, by this conventional system, 

 the number of ounces of precious metal in a ton of ore may 

 be known according to the amount of milligrammes, &c., 

 the button of precious metal weighs. 



Thus, in America, a conventional assay ton (A.T.) weigh- 

 ing 29 '166 grammes may be used (where 2,000 Ibs. = 1 

 ton); or in British countries one weighing 32-667 grammes 

 (where 2,240 Ibs. = 1 ton). Still, there is no occasion to 

 know the exact weight of the piece of metal used as an 

 A.T., so long as the operator knows how to read a balance 

 where A.T.'s are made use of. 



If 1 A.T. of ore yields a button of 1 milligramme, a ton 

 of ore yields 1 oz. troy of precious metal. 



One-tenth A.T. is a very convenient quantity of ore to 

 take ; for if the button weighs x milligrammes, this repre- 

 sents 10 x oz. of precious metal per ton of ore. 



In the absence of a proper balance, the following may be 

 of service : 



Procure from a carpenter a very thin strip of pine wood 

 (about one foot or fifteen inches long and one-third of an 

 inch wide). Place a fine needle across by means of wax, or 

 through the middle. Next obtain a piece of sheet tin or 

 other metal (one inch by half-inch), and bend its edges up 

 perpendicularly one quarter-inch on each side. On these 

 upturned portions place the needle ends. Should the beam 



